Published: Journal of Analytical Toxicology, Volume 23, Number 4, July/August 1999, pp.286-289.

Automated Extraction for the Analysis of 11-nor-D⁹- Tetrahydrocannabinol-9-Carboxylic Acid (THCCOOH) in Urine Using a Six-Head Probe Hamilton Microlab 2200 System and Gas Chromatography–Mass Spectrometry
Paul D. Whitter, Paul L. Cary, John I. Leaton, and Jim E. Johnson

An automated extraction scheme for the analysis of 11-nor-D ⁹-tetrahydrocannabinol-9-carboxylic acid using the Hamilton Microlab 2200, which was modified for gravity-flow solid-phase extraction, has been evaluated. The Hamilton was fitted with a six-head probe, a modular valve positioner, and a peristaltic pump. The automated method significantly increased sample throughput, improved assay consistency, and reduced the time spent performing the extraction. Extraction recovery for the automated method was > 90%. The limit of detection, limit of quantitation, and upper limit of linearity were equivalent to the manual method: 1.5, 3.0, and 300 ng/mL, respectively. Precision at the 15-ng/mL cut-off was as follows: mean = 14.4, standard deviation = 0.5, coefficient of variation = 3.5%. Comparison of 38 patient samples, extracted by the manual and automated extraction methods, demonstrated the following correlation statistics: r = .991, slope 1.029, and y-intercept –2.895. Carryover was < 0.3% at 1000 ng/mL. Aliquoting/extraction time for the automated method (48 urine samples) was 50 min, and the manual procedure required approximately 2.5 h. The automated aliquoting/extraction method on the Hamilton Microlab 2200 and its use in forensic applications are reviewed.

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